Crankcase compression type two-cycle engine

Abstract

The present invention provides a crankcase compression type two-cycle engine which has a comparatively simple construction, is capable of operating at a low fuel consumption and discharges an exhaust gas having a comparatively low hydrocarbon concentration. The engine comprises a crankcase, a piston, a cylinder joined to the crankcase and provided in its lower part with an exhaust port which is opened and closed by the piston, a cylinder head attached to the upper end of the cylinder, and forming a combustion chamber together with the cylinder and the piston. A poppet scavenging valve is provided in the upper part of the cylinder so as to be opened to the combustion chamber side. A diaphragm actuator operates the poppet scavenging valve using the pressure within the crankcase. The diaphragm actuator is provided with a diaphragm that receives the pressure within the crankcase on one side thereof and receives the pressure of a spring on the other side thereof. Further, a passage for introducing the pressure within the crankcase into the diaphragm actuator is connected to a scavenging passage. A fuel supply system may be connected to the scavenging passage to supply the fuel into the scavenging passage.

What is claimed is: 
     
       1. A crankcase compression type single-cylinder two-cycle engine comprising: a single crankcase;   a single cylinder communicating with said single crankcase;   a piston slidably mounted in said cylinder for movement between a top dead center position and a bottom dead center position, said piston partitioning said cylinder into a combustion chamber and a crank chamber, said combustion chamber having a first end adjacent said crank chamber and a second end remote from said crank chamber;   an air inlet opening into said crank chamber via a check valve;   an exhaust port provided in said first end of said combustion chamber;   a scavenging intake port provided in said first end of said combustion chamber adjacent said exhaust port and being in communication with said crank chamber;   an intake port opening into said second end of said combustion chamber, said intake port confronting an end of said piston;   a poppet type scavenging valve movably mounted in said intake port and confronting said end of said piston so as to be movable towards and away from said end of said piston;   a scavenging valve operating mechanism operably connected to said scavenging valve for opening said scavenging valve when said piston is located adjacent said bottom dead center position;   a scavenging passage communicating said intake port with said crank chamber; and   a fuel supply device communicating with said scavenging passage upstream of said intake port.   
     
     
       2. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, further comprising means for opening and closing said exhaust port and said scavenging intake port such that opening of said scavenging intake port is offset in time relative to opening of said exhaust port, and closing of said scavenging intake port is offset in time relative to closing of said exhaust port.   
     
     
       3. A crankcase compression type single-cylinder two-cycle engine as recited in claim 2, wherein said scavenging intake port, said intake port and said exhaust port together constitute a means for carrying out scavenging from both said first end and said second end of said combustion chamber.   
     
     
       4. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein said scavenging intake port, said intake port and said exhaust port together constitute a means for carrying out scavenging from both said first end and said second end of said combustion chamber.   
     
     
       5. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein said scavenging valve operating mechanism comprises an electromagnetic solenoid operably connected to said scavenging valve, and a crank angle sensor operably coupled with said electromagnetic solenoid.   
     
     
       6. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein said scavenging valve operating mechanism comprises a scavenging valve chamber, a diaphragm operably coupled with said scavenging valve and partitioning said scavenging valve into a pressure chamber and a valve chamber, said pressure chamber being communicated with said crank chamber to receive pressure therefrom, and a spring biasing said scavenging valve towards a closed position.   
     
     
       7. A crankcase compression type single-cylinder two-cycle engine as recited in claim 6, wherein said pressure chamber is communicated with said crank chamber via said scavenging passage.   
     
     
       8. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein said fuel supply device comprises a carburetor connected to said scavenging passage via a reed valve.   
     
     
       9. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein said fuel supply device comprises a fuel injector disposed in said scavenging passage, and a fuel pump operably connected to said fuel injector.   
     
     
       10. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, further comprising a throttle valve mounted in said scavenging passage.   
     
     
       11. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, further comprising at least one additional intake port opening into said second end of said combustion chamber, said at least one additional intake port confronting said end of said piston; and   at least one additional poppet type scavenging valve movably mounted in said at least one additional intake port and confronting said end of said piston so as to be movable towards and away from said end of said piston.   
     
     
       12. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein said air inlet opening is an air-only inlet opening for allowing only air to flow into said crank chamber.   
     
     
       13. A crankcase compression type single-cylinder two-cycle engine as recited in claim 12, wherein upon downward movement of said piston toward said bottom dead center position, the air introduced into said crank chamber through said air inlet opening is compressed, a first portion of the compressed air is forced to flow into said combustion chamber through said scavenging intake port, and a second portion of the compressed air is forced to flow to said intake port through said scavenging passage.   
     
     
       14. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein upon downward movement of said piston toward said bottom dead center position, the air introduced into said crank chamber through said air inlet opening is compressed, a first portion of the compressed air is forced to flow into said combustion chamber through said scavenging intake port, and a second portion of the compressed air is forced to flow to said intake port through said scavenging passage.   
     
     
       15. A crankcase compression type single-cylinder two-cycle engine as recited in claim 1, wherein said fuel supply device is disposed in said scavenging passage between said intake port and said crank chamber.